The development of solid state semiconductor technology has led to a vast improvement in the design of ignition systems for internal combustion engines. Rotating mechanical distributors in combination with a breaker and breaker points to synchronize fuel ignition with engine operation have been replaced by solid state electronic ignition systems of the inductive and capacitive types. Known capacitive discharge ignition systems often employ the rectified output from a magneto or similar A.C. generator to charge capacitor units which are then discharged by means of a solid state switching circuit into the primary coil of an ignition transformer. As the development of solid state capacitive discharge systems has progressed, improved timing and pulse distribution assemblies have been incorporated into the electronic switching circuitry to obtain enhanced synchronization between engine speed and fuel injection. U.S. Pat. Nos. 3,311,783 to Gibbs et al and 3,587,550 to Zechlin both disclosed electronic ignition control systems with a magnetic timing pulse source driven in correlation to the crankshaft of an engine to generate timing pulses which control the interval during which an ignition trigger pulse is applied to a rotating pulse distributor. Although such timing and pulse distribution systems operate effectively, it has often required complex mechanical or electrical adjustment to vary the timing provided by the ignition system. In some instances where timing variations have to be accomplished in response to a multiplicity of engine and ambient conditions, microprocessor technology must be employed to obtain effective programmable timing.
Also, known solid state capacitive discharge ignition assemblies have been configured in such a manner that the system may not be removed from an engine for servicing and then replaced without retiming the engine to reestablish the desired ignition/engine timing. This generally involves moving the engine from the random position where it last stopped to the number one cylinder position for retiming, and constitutes an additional, time consuming step in ignition system maintenance.
The magnetos developed for use with modern solid state ignition systems have been provided with windings of different types to furnish effective operation over a wide range of engine speeds. Generally a high speed coil is provided having a low number of turns to generate voltage at high speeds, while a low speed coil having a large number of turns is provided to generate voltage at low speeds. Multiple coil magneto systems of this type are shown by U.S. Pat. Nos. 3,861,373 to Allwang et al and 3,974,816 to Henderson et al.
One problem experienced with multiple coil magnetos capable of conducting over a wide range of engine speeds is that switching elements in the solid state ignition circuit powered by the magneto, such as silicon controlled rectifiers (SCR's) used to control the application of power pulses to the ignition transformers, may not shut off properly, thereby causing the ignition circuit to malfunction. The magneto which operates over a wide speed range is capable of generating a continuous current, and this, in combination with the energy stored in the ignition transformers, can cause current to be supplied to the control SCR's at all times. The turn off characteristic of an SCR is such that the current thereto must reduce almost to the zero level before resetting occurs. Therefore, the potential to provide a substantially constant current to the SCR can result in frequent malfunction.
Magnetos having multiple coils of different types must often be housed within large housings which are difficult to install in the space available on an engine. This is due to the fact that the high turn coils generate high heat losses, and to reduce these losses it is necessary to make the volume used for the coil winding as large as possible. The sacrifice in space required to maintain reduced operating temperatures is often not acceptable for many ignition systems applications.
It has been found to be important to provide solid state electronic ignition systems with safety and shutdown controls which operate in response to devices external to the ignition system. U.S. Pat. Nos. 3,418,990 to Lindell, 4,034,732 to Van Burkleo, 4,193,385 to Katsuma et al, and 4,246,493 to Beeghly all disclose safety and shutdown systems of known types. Conventional shutdown systems for capacitive discharge solid state ignition systems take power from the ignition system power capacitor and thereby reduce the energy available for spark ignition. With modern microprocessor engine control systems, it has become more desirable to provide safety and shutdown units which do not reduce the energy level available for ignition.
Finally, with present solid state ignition systems, it is possible to inadvertently short out or ground the primary side of the ignition transformers and thereby damage the control SCR's and system capacitors. In practice, the wiring for the ignition transformers is not done during the manufacture of the magneto and solid state ignition system, but is done later by the end user or engine manufacturer. If this subsequent wiring is improperly accomplished, transformer shorting is likely.